With the ever increasing technical developments in highenergy electron-beam radiation sources, there has also been an increased need for more complex and varied magnetic field configurations in permanent magnet solenoids. For example in some electron-beam devices such as gyro amplifiers, a stepped magnetic field with a narrow transition is desirable.
In order to produce such a magnetic field it would be obvious to place in tandem two permanent magnetic solenoids such as those disclosed in U.S. Pat. No. 4,647,887, issued to Leupold on March 3, 1987, entitled, "Lightweight Cladding For Magnetic Circuits," or in U.S. Pat. No. 3,768,054 issued to Neugebauer and entitled, "Low Flux Leakage Magnetic Construction." Neugebauer discloses a permanent magnet solenoid wherein the leakage of magnetic flux of a first magnet is prevented by placing a second permanent magnet adjacent the first magnet with the magnetic axis of the second magnet perpendicular to the axis of the first magnet. Leupold discloses a permanent magnet structure which comprises, in combination, a longitudinally extending first magnet having a longitudinal magnetic polarity, a second magnet surrounding a substantial portion of the length of the first magnet, and having a generally radial magnetic polarity transverse to the longitudinal magnetic polarity of the first magnet, the second magnet also having a constant magnetic potential on its outer surface of the first magnet at a circumferential portion between the ends thereof.
Placing either one of these structures in tandem with itself as shown in FIG. 3 would produce a stepped magnetic field which would be useful in such applications as a gyro amplifier. However, the magnetic field produced by such a structure would not be ideal for a gyro amplifier because the transition between the two fields would be relatively gradual.